The purpose of this multi-center sub-study of the U.S. CDC Rifapentine Clinical Trial (USPHS Study 22) was to evaluate drug pharmacokinetics and risk factors for relapse among four patient groups: 1. HIV-positive patients, 2. those who failed TB treatment or relapsed, 3. HIV-negative controls, matched to each HIV-negative failure or relapse, and 4. all HIV-negative participants on study-phase therapy in the Rifapentine Clinical Trial (referred to as the prospective group). This pharmacokinetic sub-study was initiated following rifampin-resistant TB relapse which occurred in 4 of the 36 HIV-positive patients who received rifapentine in Study 22. The study was done on the General Clinical Research Center (GCRC). After informed consent was obtained, each patient received a single dose of INH and either rifampin or rifapentine (whichever they received in the study phase of the Rifapentine Clinical Trial). Patients on protease inhibitors did not receive either rifamycin. For patients who were currently receiving therapy in the Rifapentine Clinical Trial, blood was drawn just prior to the medication dose. Blood was drawn at 1, 2, 5, and 24 hours post dose. Patients who received rifapentine also had blood drawn at 48 hours post dose. Blood was also drawn for INH acetylator status, CBC, chemistries, and for those HIV-positive, for CD4 count and HIV viral load. Urine was collected at 5 and 24 hours post dose. Plasma for acetylator status, pharmacokinetics, and viral load was frozen and shipped to a central lab for testing. The medical record was reviewed and patients interviewed regarding concomitant medications, gastrointestinal symptoms, and meals. Patients were asked to duplicate, as much as possible, the meals and medications they took during study-phase therapy. Data management and analysis will be done by CDC. A primary analysis among HIV-positive patients will compare rates of relapse and of rifampin-resistant relapse by INH acetylator status. Univariate analyses will consider pharmacokinetic characteristics of each subject.